Mara Jacqueline Willaford, left, holds her fist overhead as Democratic presidential candidate Sen. Bernie Sanders, I-Vt., stands nearby at a rally Saturday. The activists took over the microphone and refused to allow Sanders to speak.

Elaine Thompson/AP

Democratic presidential candidate Bernie Sanders found himself involuntarily sidelined at a rally Saturday night in Seattle, as Black Lives Matter activists commandeered the microphone and refused to give it back.

Sanders had just begun to speak at the conclusion of a Social Security Works rally at Westlake Park when two women climbed on stage and took over the microphone. They demanded that the crowd hold Sanders "accountable."

Some in the crowd booed.

"I was going to tell Bernie how racist this city is, filled with its progressives, but you already did it for me. Thank you," one of the activists said. Then she called for 4 1/2 minutes of silence for Michael Brown, but part of the crowd began shouting "Let Bernie speak."

"After sharing a few local grievances with the crowd, including school disparities and gentrification in Seattle, the protesters asked for a period of silence to commemorate the one-year anniversary of Michael Brown being shot and killed during a confrontation with a police officer in Ferguson, Mo.

"Event organizers allowed the period of silence, as some in the large crowd booed and shouted for the protesters to leave the stage. Afterward, Marissa Janae Johnson, who identified herself as a leader of the Black Lives Matter chapter in Seattle, asked the crowd to "join us now in holding Bernie Sanders accountable for his actions." She motioned for Sanders to join her at the microphone."

After about 20 minutes, "Sanders himself was pushed away when he tried to take the microphone back," KOMO reports.

Eventually, the organizer of the event announced it was over and Sanders gave a clenched-fist salute to the crowd and waved goodbye.

Hours later, the Democratic presidential candidate spoke to a packed crowd at the University of Washington campus.

At the campus rally, Sanders told the crowd that as president he would "fight harder to end institutional racism and reform criminal justice system," according to the King5-TV station. "Too many lives have been destroyed by war on drugs, by incarceration; we need to educate people. We need to put people to work."